1. The water, ash, glycogen, nitrogen, and ether extract content of the tissues of chicken embryos were determined between the 5th and the 19th days of incubation.
2. It was found that the concentration of solid substance changed from approximately 5 to 17 per cent during this interval. The chief change in the organic substances involved a relative decrease in the nitrogen as compared with the fat.
3. Bomb calorimetric estimations confirmed these findings. It was shown that the calorific value of the dried substance increased with age.
4. The rate of growth of the total solids, and of the potential energy of the tissues was estimated.
5 Various theoretical considerations were brought forward dealing chiefly with the order in which the chief organic substances, carbohydrate, protein, and fat could be ranged when judged by various criteria.